1. Field of the Invention
This invention relates to a femur prosthetic device. More particularly, this invention relates to a hip prosthesis adapted for insertion into the upper medullary canal in the femur of a patient. The hip prosthesis of this invention is of the type generally characterized as including a head or ball member, a shaft member for insertion into the intermedullary canal, and a neck member connecting the ball and shaft or stem member, and also including at least one porous metal surface portion which provides for stabilization by bone ingrowth without requiring any cement.
2. Description of the Prior Art
Hip prostheses are known in the art and these have included various design configurations of the various components, including the head member, neck, collar and shaft. Both straight and curved shafts as well as fluted shafts are known. Representative of these known hip prostheses are those described in the following: U.S. Pat. No. 4,279,042--T. P. Andriacchi, et al; U.S. Pat. No. 3,965,490--I. P. Murray, et al; U.K. Patent Application, G.B. No. 2,069,340A--K. Hardinge. Known commercial products include the Bard Contour.TM. and Link SP-femoral hip prosthesis, manufactured by Waldemar Link Hamburg, West Germany and the Isoelastique Butel hip prosthesis by Butel, Grenoble, France.
Prosthetic devices provided with porous surfaces for bone ingrowth are also known, e.g. U.S. Pat. No. 3,906,440--W. Rostoker, et al and British Pat. Spec. No. 1,554,454--J. C. Bokros.
Nevertheless, further improvements in the total design of hip prosthesis are required to assure stable fixation of the implanted prosthesis at the bone/metal interface. Thus, in cemented prosthetic devices there has not been satisfactory fixation due to the various stress loads, i.e. compression, shear and torsion, to which the implanted device is subjected. These mechanical forces, especially shear and torsion, weaken the bone cement bond. In addition, it is known that there is a tendency for bone resorption which also weakens the cement bond between the bone, e.g. intramedullary canal of the femur, and the femoral prosthesis.
On the other hand, by providing a bone ingrowth surface on the prosthetic device a more stable fixation would be expected and some advances along these lines have been made. However, experiments by the present inventors have shown that bone ingrowth requires the prosthesis to be stably fixed without movement for at least six weeks and any relative motion of the prosthesis during that period prevents or minimizes bony ingrowth.
As a result, an incidence of ten to twenty percent of femoral stem loosening or failure in total hip arthroplasty patients followed over 5 or more years, especially in younger patients, has been reported.